Скачать или смотреть Fixing Python Stack Print Issues: Your Stack Object Should Display Actual Values, Not Addresses

Learn how to customize the print behavior of your Stack object in Python by implementing the `__str__` and `__repr__` methods for better output display.
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This video is based on the question https://stackoverflow.com/q/66686403/ asked by the user 'MûHammad UMar' ( https://stackoverflow.com/u/15051922/ ) and on the answer https://stackoverflow.com/a/66686996/ provided by the user 'lllrnr101' ( https://stackoverflow.com/u/14904573/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing Python Stack Print Issues: Your Stack Object Should Display Actual Values, Not Addresses

When working with custom objects in Python, you might run into a situation where printing the object returns an address instead of the actual values you expect. This can often be confusing, especially when you want to see the contents of your Stack class, but instead, you're just seeing memory references. This post will explain how to resolve this issue and ensure that your Stack object provides meaningful output.

The Problem

If you have defined a simple Stack class but notice that printing the object only returns its memory address, the reason behind this behavior lies in how Python handles object representation. By default, Python uses the built-in methods to generate a string that represents an object. If you haven't defined any specific methods for string representation, Python will return the address instead.

Example of the Default Behavior

Consider this snippet of your Stack implementation:

[[See Video to Reveal this Text or Code Snippet]]

When you try to print an instance of this Stack, it does not show the contents of _theItems but instead provides an output similar to:

[[See Video to Reveal this Text or Code Snippet]]

This behavior is not helpful when trying to debug or check the contents of your Stack.

The Solution

To display the actual contents stored in your Stack object, you need to implement two special methods in your class: _str_ and __repr__. Let’s break these down:

Step 1: Implement _str_ Method

The _str_ method is called by the print() function and is used to represent the object in a human-readable format. Here is how you can implement it:

[[See Video to Reveal this Text or Code Snippet]]

This method tells Python how to convert your Stack object to a string whenever it's printed, providing a descriptive output.

Step 2: Implement _repr_ Method

The _repr_ method is meant to provide a formal string representation of the object, which is typically used for debugging. It’s common to have _repr_ return the same value as __str__, especially for simple classes:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Modify the Display Method

You can modify your existing display() method to call __repr__, which is now effective for whole object representation:

[[See Video to Reveal this Text or Code Snippet]]

Complete Revised Class Example

Here’s how your Stack class should look after modifications:

[[See Video to Reveal this Text or Code Snippet]]

When you run your modified code, you will see an output like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By implementing the _str_ and _repr_ methods in your Stack class, you can ensure that printing your Stack instance will give you the actual values contained in it rather than just a memory address. This simple enhancement will significantly improve the usability and readability of your Stack class, making debugging much easier. Happy coding!